1. Field of the Invention
This invention relates to a power transmission belt. More particularly, the invention relates to a power transmission belt which comprises a compression layer and an adhesive rubber layer both of which are formed of a vulcanizate of an ethylene-xcex1-olefin-diene rubber compound and which has a plurality of load carrying cords formed of aramid fibers (which are referred to as xe2x80x9caramid fiber cordsxe2x80x9d hereunder) embedded in the adhesive rubber layer, and which is excellent both in durability and strength. The invention further relates to a process for the production of such a power transmission belt.
2. Description of the Prior Art
In general, a power transmission belt comprises a compression layer and an adhesive rubber layer, and a plurality of load carrying cords, i.e., fiber cords, are adhered to and embedded in the adhesive rubber layer. Optionally, the belt has a rubberized canvas or reinforcing fabric on the upper face or the inner face or on the whole surfaces including the side faces.
For the production of a power transmission belt, in particular, a compression layer of the belt, chloroprene rubber or a mixture of hydrogenated nitrile rubber and chlorosulfonated polyethylene rubber has been used heretofore. However, in recent years, an attempt has been made to use ethylene-xcex1-olefin-diene rubber for the production of an adhesive rubber layer as well as a compression layer to meet a demand of xe2x80x9cchlorine freexe2x80x9d products from the standpoint of environmental protection.
However, as known in the art, ethylene-xcex1-olefin-diene rubber has a defect that it is inferior in dynamic properties, in particular, in resistance to fatigue and wear, tensile strength and elasticity. In addition, it has poor adhesion to load carrying cords of aramid fibers. Such being the case, it has been considered difficult to use ethylene-xcex1-olefin-diene rubber to produce power transmission belts in which dynamic properties are important requisites.
The present inventors have made intensive investigation to realize a power transmission belt which is excellent both in durability, i.e., dynamic life, and strength and which comprises a compression layer and an adhesive rubber layer both of which are formed of ethylene-xcex1-olefin-diene rubber compound and which has a plurality of load carrying cords formed of aramid fibers bonded to and embedded in the adhesive rubber layer. As results, the inventors have found that the treatment of the aramid fiber cords having a first twisting coefficient and a final twisting coefficient both in the range of from 650 to 950 with a resorcin-formalin-latex adhesive composition wherein the latex in the composition contains at least one of a chlorosulfonated polyethylene and an alkylated chlorosulfonated polyethylene therein as solid components (rubber components) provides excellent dynamic adhesion between the aramid fiber cords and the adhesive rubber layer.
Thus, they have obtained a power transmission belt which is excellent both in dynamic properties and strength and which comprises a compression layer and an adhesive rubber layer both of which are formed of ethylene-xcex1-olefin-diene rubber compound and which has a plurality of aramid fiber cords bonded to and embedded in the adhesive rubber layer. In this manner, they have completed this invention.
The inventors have further found that use of resorcin-formalin-latex adhesive composition which contains a specific metal oxide and a sulfur containing vulcanization accelerator for treatment of the aramid fiber cords further improves dynamic adhesion between the aramid fiber cords and the adhesive rubber layer even if the aramid fiber cords are dipped in the adhesive composition and dried at a temperature as high as 210xc2x0 C. or more, and that they accordingly can manufacture power transmission belts formed of ethylene-xcex1-olefin-diene rubber and having aramid fiber cords embedded therein in a very high productivity.
The invention has been completed to solve the above-mentioned problems in the known power transmission belts formed of ethylene-xcex1-olefin-diene rubber. Accordingly, it is an object of the invention to provide a power transmission belt which comprises a compression layer and an adhesive rubber layer which are formed of ethylene-xcex1-olefin-diene rubber and adhered to each other by vulcanizing together and, which comprises aramid fiber cords adhered to and embedded in the adhesive rubber layer, and which is excellent both in durability and strength.
It is a further object of the invention to provide a process for the production of a power transmission belt as mentioned above.
The invention provides a power transmission belt which comprises a compression layer and an adhesive rubber layer which are adhered to each other by vulcanizing together and which has a plurality of aramid fiber cords having a first twisting coefficient and a final twisting coefficient both in the range of from 650 to 950 and embedded in the adhesive rubber layer, wherein the compression layer and the adhesive rubber layer are formed of vulcanizate of an ethylene-xcex1-olefin-diene rubber compound and wherein the aramid fiber cords are adhesion treated with a resorcin-formalin-latex adhesive composition wherein the latex contains at least one of chlorosulfonated polyethylene and alkylated chlorosulfonated polyethylene in an amount of 50-100% by weight based on the solid components (rubber components) of the latex, and adhered to and embedded in the adhesive rubber layer.
The invention further provides a process for production of a power transmission belt which comprises a compression layer and an adhesive rubber layer which are adhered to each other by vulcanizing together and which has aramid fiber cords embedded in the adhesive rubber layer, which comprises:
carrying out adhesion treatment of the aramid fiber cords having a first twisting coefficient and a final twisting coefficient both in the range of from 650 to 950, wherein the adhesion treatment comprises impregnating the aramid fiber cords with a resorcin-formalin-latex adhesive composition wherein the latex contains at least one of chlorosulfonated polyethylene and alkylated chlorosulfonated polyethylene in an amount of 50-100% by weight based on the solid components of the latex as well as at least one metal oxides and at least one sulfur containing vulcanization accelerators, and heating and drying the resulting aramid fiber cords at a temperature of 210-260xc2x0 C.;
placing the resulting aramid fiber cords between a pair of sheets formed of unvalcanized ethylene-xcex1-olefin-diene rubber compound which is to form an adhesive rubber layer;
laminating the said pair of sheets formed of unvalcanized ethylene-xcex1-olefin-diene rubber compound on a sheet formed of unvalcanized ethylene-xcex1-olefin-diene rubber compound which is to form a compression layer; and
heating the resulting laminate under pressure to vulcanize the laminate in a body to provide the belt wherein the aramid fiber cords are adhered to and embedded in the adhesive rubber layer.